Patients with RA + osteoporosis had higher sRANKL levels (1063.7 vs. 602.3 pmol/L, p = 0.005), higher sRANKL/OPG ratio (14.1 vs. 7.6, p = 0.017), lower serum concentrations of DKK-1 (204.1 vs. 279.4 pg/mL, p = 0.028), and decreased serum SOST levels compared with RA patients without osteoporosis (114.1 vs. 163.5 pg/mL, p < 0.001). Here, DKK1 is linked to osteoporosis.